1. Field of the Invention
This invention relates to apparatus and methods for cleaning magnetic data storage tapes. The present invention is particularly useful for removing minuscule particles from the surface of magnetic tape employed in extremely high data density applications.
2. Description of the Prior Art
The sensitivity to debris, or contaminants, of magnetic tape drives that read and write digital data on magnetic tape is a function of the density of the data on the tape, and the size of the contaminating particles. Early systems with relatively low data packing densities were fairly tolerant of dust sized particles. Such particles, when ionized, tend to be attracted to the surface of the magnetic tape. However, they were not a serious impediment to data transfers by early read/write heads. Since, at most, one bit of data was normally lost, recovery was possible by error correction without reversing the drive and/or by re-reading the tape sections where data was not properly sensed. In higher density systems, loss of several bits of data may defy reconstruction and, at the very least, demand stopping, repositioning and re-reading of the tape. This procedure increases the overall data throughput time of the system.
In high density storage tapes, even a small amount of foreign matter can significantly reduce the number of tracks available for recording on the tape. Worse yet, such particles cause random losses of data in reading, thereby increasing data processing throughput time as well as hazarding lost data. In addition, particles from the tape can cause wear to the tape reader heads, and reduce the life of the machine.
Because of the manufacturing techniques used by tape manufacturers, new manufactured tapes contain a significant amount of particulate debris. For example, the screws used to hold the cassettes together are added after the tape is in place, abrading off particles of metal and plastic. Also, stored or archived tapes tend to collect dirt and dust. The dust falls off into the machine, eventually damaging it, and sticking to other tapes loaded into the machine later.
Prior art tape cleaning mechanisms include U.S. Pat. No. 4,930,033 by Pergerson, which teaches running the tape over a scrapper and through two wiper stations. In addition, U.S. Pat. Nod. 4,408,203 by Bonner et al., 4,185,306 by Dudley, and 4,713,857 by Cecile et al are all variations on bringing a wiping medium into contact with the moving tape.
These prior art tape cleaning devices suffer from a variety of disadvantages. There is no air flow to pull the particles away as they are wiped off. In addition, they fail to deionize the particles so they will not cling to the tape after they are dislodged by the wiping action. The particles may stick to the tape after wiping, or be attracted right back to the surface of the tape. Also, the particles may fall into the machine, causing wear and eventually damaging its working parts, and sticking to other tapes placed in the machine. U.S. Pat. No. 4,454,621 by Testone discloses removing charged particles from a web of textile material by discharging the web with an ionized air flow from ion generators that surround the web. The intent is to remove the particles by the air flow. This patent is not directed at the field of cleaning high density magnetic data tapes, nor does it combine wiping of the surface with an ionized air flow. The air flow is not filtered or recirculated.
No prior art device has functioned satisfactorily to remove minute particles from the surface of magnetic tape designed to handle high density digital data packing.